1. Field of the Invention
Broadly, this invention relates to a microwave apparatus or oven having a cavity and a coaxial feed or transition that extends from an external waveguide to a rotating antenna applicator inside the cavity. In particular, the invention relates to an annular knob that surrounds the coaxial feed and is positioned on the top of the rotating antenna applicator. The annular knob is adapted to suppress the radial leakage, uncontrolled excitations and arcing that occurs within the cavity.
2. Description of Related Art
Microwave cavities may have a coaxial feed or transition from an external waveguide to a rotating antenna applicator inside the microwave cavity. Typically, the coaxial feed is attached to the external waveguide and is disposed through an aperture in the ceiling of the cavity so that it terminates within the rotating antenna applicator. To allow rotation of the antenna applicator, a coaxial gap is provided between the coaxial feed and the rotating antenna applicator and a gap region is provided between the rotating antenna applicator and the ceiling of the microwave cavity. The presence of the coaxial gap permits microwave energy to escape from the antenna applicator (radial leakage). This radial leakage causes uncontrolled excitation of modes and occasional arcing in the gap region between the rotating antenna applicator and the ceiling of the microwave cavity. Accordingly, it is advantageous to suppress the radial leakage from the coaxial gap and suppress the excitations and arcing in the gap region.
Prior attempts have been made to suppress these leaks and excitations by minimizing the coaxial gap and the gap region. Essentially, the correspondence or "fit" between the coaxial feed and the opening in the rotating antenna applicator was adjusted to make the coaxial gap smaller. Likewise, the length of the coaxial feed was reduced so that the gap region between the rotating antenna applicator and the ceiling of the microwave cavity was made smaller. While these attempts partially suppressed the radial leakage and uncontrolled excitations, they caused other problems. First, the smaller coaxial gap and the gap region often caused improper rotation or impeded the rotation of the antenna applicator. Also, a great deal of precision was required, thus causing this solution to be expensive. Still further, with the smaller coaxial gap and the gap region, cleaning became more difficult.